In order to meet the demand for wireless data traffic soaring since the 4G communication system came to the market, there are ongoing efforts to develop enhanced 5G communication systems or pre-5G communication systems. For the reasons, the 5G communication system or pre-5G communication system is called the beyond 4G network communication system or post LTE system.
For higher data transmit rates, 5G communication systems are considered to be implemented on ultra-high frequency bands (mmWave), such as, e.g., 60 GHz. To mitigate pathloss on the ultra-high frequency band and increase the reach of radio waves, the following techniques are taken into account for the 5G communication system: beamforming, massive multi-input multi-output (MIMO), full dimensional MIMO (FD-MIMO), array antenna, analog beamforming, and large-scale antenna.
Also being developed are various technologies for the 5G communication system to have an enhanced network, such as evolved or advanced small cell, cloud radio access network (cloud RAN), ultra-dense network, device-to-device (D2D) communication, wireless backhaul, moving network, cooperative communication, coordinated multi-point (CoMP), and interference cancellation.
There are also other various schemes under development for the 5G system including, e.g., hybrid FSK and QAM modulation (FQAM) and sliding window superposition coding (SWSC), which are advanced coding modulation (ACM) schemes, and filter bank multi-carrier (FBMC), non-orthogonal multiple access (NOMA) and sparse code multiple access (SCMA), which are advanced access schemes.
Conventional mobile communication systems, 3GPP LTE and LTE-A, have been designed assuming that they are served on licensed frequency bands. Licensed band frequencies have been able to serve efficiently through their exclusive use.
However, as mobile communication systems go beyond voice-centered services that they initially intended and are involving soaring use of high-speed, high-quality wireless packet data, a need comes along to increase the capacity. An approach to increase the overall capacity of mobile communication system may be to enable the LTE-A system to operate on shared bands, in particular, unlicensed bands.
Meanwhile, since shared bands cannot be in exclusive use, if a particular frequency at which LTE-A system operates belongs to a shared band, such a case may arise that some LTE-A subframes cannot be used due to use restrictions on the unlicensed band or transmission by other wireless transmitters that are sharing the unlicensed band.
A communication system using an unlicensed band frequency should discontinuously or in chances use the unlicensed band frequency to co-exist with neighbor unlicensed band systems. Accordingly, transmission reliability may be lowered in control channels and shared channels used in mobile communication system.